A gas turbine engine such as that used for powering an aircraft includes rotor blades such as those found in a compressor thereof which are suitably fixedly joined to a rotor disk for accommodating centrifugal and aerodynamic loads generated during operation. As the rotor disk rotates during operation, the blades joined thereto are centrifuged radially outwardly, with the centrifugal loads generated thereby being suitably channeled to the rotor disk at stresses below predetermined stress limits for ensuring an effective useful life of the bladed disk combination.
More specifically, the blade includes a dovetail which is retained in a complementary dovetail groove in the perimeter of the motor disk for retaining the blade thereto during operation. The blade dovetail may either be an axial-entry type which is disposed in a complementary axially extending dovetail groove in the rotor disk, or may be a circumferential-entry type disposed in a complementary circumferentially extending groove in the perimeter of the rotor disk. In the latter case, for example, the blade dovetail has a width extending in the circumferential direction which is suitably large to provide a broad support for stabilizing the blade in the disk during operation and for obtaining acceptable stress levels therein. As the dovetail width is made larger, the stresses therein due to centrifugal force acting on the blade airfoil typically decrease, but, however, the centrifugal loads from the dovetail itself will increase which typically requires a larger disk perimeter for accommodating all of the centrifugally induced loads of the dovetail and airfoil while maintaining acceptable levels of stress therein.
The width of a circumferential entry dovetail is conventionally determined in one design as approximately equal to the rotor disk circumference divided by twice the total blade count minus twice the corner radius of the loading slot through which each of the dovetails is initially radially inserted into the rotor disk prior to being circumferentially positioned along the circumference of the dovetail groove. As the diameter of the rotor disk increases for larger engine designs relative to the number of blades used in a blade row, the resulting width of each dovetail in accordance with this conventional practice is more than that required to meet acceptable stress levels. In other words, the dovetail width becomes larger and, therefore, the shank reaction stresses therein become substantially small. However, the relatively large dovetail itself increases centrifugal loads which must be carried by the rotor disk, which, therefore, requires a larger disk to accommodate the centrifugal loads within acceptable stress limits. Accordingly, a lightweight dovetail is desired for this large diameter rotor disk application wherein the conventional dovetail width may be maintained, but with reduced weight thereof and acceptable reaction stresses therein for obtaining a useful life in a gas turbine engine application.